Direct observation of local strain field for ULSI devices

Abstract

The in-depth profile of strain distribution from the silicon surface is one of the most important pieces of information for optimizing the device performance. The convergent-beam electron diffraction(CBED) method has been applied to analyze the local strain filed of the active regions for both test structure with the shallow trench isolation(STI) and the conventional LOCOS on a cross-sectional surface. As a result, strain distribution was observed successfully. It was found that the compressive stress exist all over the survey regions. The active region close to the bottom corner of the STI shows a larger stress than that of the conventional LOCOS. It is demonstrated that the CBED technique is very effective for the determination oflocal strain field in a small area of semiconductors and the optimizing of the STI structure andfabrication process.